Setting up new account. Got locked out before setting master password. Can't log in w/o pswd.

I have been a version 4 user for years. Recently persuaded to upgrade to a monthly family subscription. I started the process, gave my credit card and signed up for a mypassword login. Got my secret key. I did not get a chance to download apps or get a new master password. I was idle and got locked out. Now I cannot log back in without a master password. Old master password does not work. What do I do?